Jul 22, 2019
Dr Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. We're your co-hosts, I'm Dr Carolyn Lam, Associate Editor from the National Heart Center and Duke National University of Singapore.
Dr Greg Hundley: And I'm Greg Hundley, Associate Editor at the Pauley Heart Center at VCU Health in Richmond, Virginia.
Well Carolyn, did you ever wonder whether cardiovascular drug effects could be investigated through natural variation in the genes for the protein targets? In our feature discussion today, investigators from the British Isles, Germany, and the United States use this approach to explore the potential side effects and repurposing potential of antihypertensive drugs. Sound interesting? Well listeners, we look forward to the results later in our program, but Carolyn, how about we chat about some of the other papers in this issue?
Dr Carolyn Lam: You bet Greg. So, have you ever asked yourself "What is the role of protein glycosylation in regulating LDL metabolism?"
Dr Greg Hundley: That was going through my mind when we were playing basketball just the other night.
Dr Carolyn Lam: Well this is truly a great study from Dr Holleboom at Academic Medical Center Amsterdam and Dr Lefeber from Radboud University Medical Center, both in the Netherlands. And their colleagues will study 29 patients of the two most prevalent types of Type 1 Congenital Disorder of Glycosylation, and these are the ALG6 and PMM2 types. They also study 23 first and second-degree relatives with a heterozygote mutation and measured their plasma cholesterol levels. LDL metabolism was studied in three cell models. They found that patients with type 1 congenital disorder of glycosylation have hypobetalipoproteinemia through increased LDL receptor expression. Carriers of the mutation in glycosylation enzymes affected in this syndrome had decreased LDL cholesterol levels compared to controls, and defects in glycosylation enzymes could play, therefore, an important role in LDL cholesterol metabolism.
Dr Greg Hundley: Boy, this is pretty insightful I think, Carolyn. So, what are the clinical implications?
Dr Carolyn Lam: Well, given that LDL cholesterol was also reduced in a group of clinically unaffected heterozygotes, the authors propose that increasing LDL receptor mediated cholesterol clearance, by targeting N-glycosylation in the LDL pathway, may therefore represent a novel therapeutic strategy to reduce LDL cholesterol, and of course prevent cardiovascular disease.
Dr Greg Hundley: Very interesting work. You know, we just keep learning more and more about LDL. I'm going to switch and jump back with Empagliflozin. And this is a study in diabetic mice that really has an interesting in-vivo imaging component. As an imager, I was really excited about this. The article is from Dr Kengo Kidokoro from Kawasaki Medical School. And we don't often talk about it, but listeners, if you have a chance, there's a very interesting video-enhanced file associated with this article, and if you can download it, it's really just so cool with multiple image clips demonstrating an operative mechanism of SGLT2 inhibition on renal function. And it really gives us an opportunity to revisit renal function.
Quick quiz Carolyn. In diabetic kidney disease, is glomerular hyperfiltration good or bad?
Dr Carolyn Lam: Bad.
Dr Greg Hundley: Yeah, absolutely. So, hyperfiltration is characteristically observed at earlier stages of diabetic kidney disease and involves activation of the renin-angiotensin-aldosterone system at the efferent arteriole and tubuloglomerular feedback mechanisms, especially at the afferent arteriole. So, as they go through this, just picture in your mind that glomerulus and afferent is arriving, and efferent is leaving.
So, SGLT2 upregulation in diabetes is thought to play an important role in TGF signaling by increasing sodium reabsorption at the proximal tubule, thereby decreasing distal delivery to the sodium sensing macula densa at the juxtaglomerular apparatus. This decline in distal sodium delivery is interpreted as a decline in effective circulating volume, leading to inappropriate afferent vasodilation in an effort to preserve intra-glomerular pressure and GFR.
In diabetes, these TGF effects lead to intra-glomerular hypertension and hyperfiltration. You got that quiz right, Carolyn. Which promotes diabetic kidney disease progression and impaired kidney function, ultimately increasing overall cardiovascular risk and mortality. Conversely, blocking SGTL2 pharmacologically reduces renal hyperperfusion and hyperfiltration in animals and humans, which may preserve renal function, thereby reducing risk associated with diabetic kidney disease progression.
Dr Carolyn Lam: You know what, Greg? I kind of had an unfair advantage in this quiz. I work with a lot with the SGLT2 inhibitors, but I just love that you asked us to picture it and look at that video. Anyways, so this article really allows us to review SGLT2 inhibition at the glomerular level, which is truly hot. So, tell us what did they find?
Dr Greg Hundley: So, this is the first report of changes in renal hemodynamic function by SGLT2 inhibition using direct in-vivo visualization techniques in a diabetic animal model. The videos, they're spectacular, and they're excellent so that you can download them for educational purposes. Afferent arteriolar vasoconstriction, and reduced hyperfiltration occurred within a few hours after a single dose of a SGLT2 inhibitor. And Adenosine signaling, through tubuloglomerular feedback, is a key pathway to prevent diabetic hyperfiltration via SGLT2 inhibition.
Clinically, Carolyn, now I know you would ask me about that, so I got ready, this study highlights another potential mechanism for the benefits of SGTL2 inhibition. The SGLT2 inhibitor-related mechanism's responsible for reducing cardiovascular risk in clinical trials may be due to protection against diabetic kidney disease progression, thereby attenuating risk factors for heart failure, such as volume overload and hypertension.
Dr Carolyn Lam: Ah. That is just so cool, and really just so consistent with the clinical data that's emerging too. Thank you, Greg. So, have you ever asked yourself this other question, what role do platelets play in ischemia reperfusion injury? So, I'm not going to quiz you. I'm actually kind and loving and a good person. And so, I will tell you about ischemia reperfusion injury, which is a common complication of cardiovascular disease.
Now, resolution of the detrimental effects of ischemia reperfusion injury generated prothrombotic and proinflammatory responses, is essential to restore homeostasis. Now, although platelets are known to play a crucial role in the integration of thrombosis and inflammation, their role as participants in the resolution of thrombo-inflammation is really under-appreciated. And hence, this other paper that I chose today, and it's from Dr Gavins from Louisiana State University Health Sciences Center Shreveport, and her colleagues, who used pharmacological and genetic approaches, coupled with murine and clinical samples to uncover key concepts underlying this role for platelets.
Dr Greg Hundley: So Carolyn, what did they find?
Dr Carolyn Lam: Well, they found that exacerbation of thrombo-inflammatory responses occurred in ischemia reperfusion injury mouse models of middle cerebral arterial occlusion, as well as lower plasma levels of the anti-inflammatory pro-resolving protein Annexin A1. And this was a lower plasma level of this Annexin A1 among patients with acute ischemic stroke.
Administration of Annexin A1 promoted cerebral protection against thrombo-inflammation and the development of subsequent thrombotic events post-stroke. Annexin A1 was also able to reduce platelet activation and thrombosis, via the suppression of integrins. So, overall, these data reveal a novel multi-faceted role for Annexin A1 to act both as therapeutic and prophylactic drug via its ability to promote endogenous pro-resolving anti-thrombo, anti-inflammatory circuits in the cerebral ischemia reperfusion injury. And collectively, these results further enhance our understanding in the field of platelet and ischemia reperfusion injury biology.
Dr Greg Hundley: Oh wow. So, another important insight from this author group on platelet activation and thrombosis in key clinically relevant syndromes. Well, my last paper is going to be talking about a risk prediction score for life-threatening ventricular tachyarrhythmias. And they're going to study this in laminopathies, and the lead investigator is Dr Karim Wahabi from Cochin Hospital in France.
To estimate the risk of life-threatening ventricular tachyarrhythmia in patients with LMNA mutations, and thus select candidates for implantable cardiac defibrillators, the investigators evaluated 444 patients of about 40 years in age in a derivation sample. And then, 145 patients that are about the same age, 38 years, in a validation sample, for the occurrence of a) sudden cardiac death or b) ICD-treated or hemodynamically unstable ventricular tachyarrhythmias.
Dr Carolyn Lam: Oh. Very important. These laminopathies are really not that uncommon. So what did they find, Greg?
Dr Greg Hundley: Carolyn, predictors of events included male sex, non-missense LMNA mutations, first-degree and higher AV block, non-sustained ventricular tachycardia, and LVEF. The authors developed a new score to estimate the 5-year risk of life-threatening ventricular tachyarrhythmias in patients with LMNA mutations. And compared to the current standard of care, the proposed risk prediction model offered more accurate prediction of life-threatening ventricular tachyarrhythmias, and correctly re-classified almost 30% of the patients in the study.
Nicely, the authors have made this available, and the score can be derived from readily collected clinical and genetic parameters and estimated using an online calculator that's provided in the journal. But, it's https://lmna-risk-vta.fr.
Future prospective studies should focus on the estimation of the clinical benefit conferred by the use of this score in terms of sudden cardiac death prevention.
Dr Carolyn Lam: That is super cool, Greg. But, I am so excited now to move to our feature discussion. Shall we?
Dr Greg Hundley: You bet.
Dr Carolyn Lam: Can we use natural variations in our genes for the protein targets as a way to look at cardiovascular drug effects? Man, this is going to be such an important and exciting discussion, because this is what our feature paper talks about. I am so pleased to have with us our corresponding author, Dr Dipender Gill from Imperial College London, as well as our Associate Editor, Dr Wendy Post from Johns Hopkins.
So, first of all, Dipender, please, could you give us a background on what you did? This is really very novel in approach.
Dr Dipender Gill: It was also a lot of fun to conduct. I think, currently, we're living in an era where there's been a recent explosion in the availability of genetic data, and this really inspired us to think about how we could use that to learn more about commonly prescribed drugs. The implementation of genetics, or genetic variance, to study drug effects isn't entirely novel. It's actually been undertaken for some years now.
Most of the work has been related to lipid lowering drugs, for example, statins, where people can take genetic variance, or versions of genes, corresponding to the drug effect, and study these to investigate what effects these drugs might have, both on the intended target, but also potential side effects. To my knowledge, this hadn't previously been done for anti-hypertensive drugs. But yet, the data for this was available. And therefore, we thought that actually we could very well go ahead and do this, and perhaps find some interesting things.
Dr Carolyn Lam: Oh, that's so interesting thing, Dipender. You know, there was this term in your abstract, and mentioned multiple times, Mendelian randomization. Now, for those of us that don't think about this every day, could you tell us a little bit what that means?
Dr Dipender Gill: Yeah. So, I'll actually give a little bit of background. One of the main limitations of traditional epidemiological research is that any association, it's sometimes difficult to infer causation. They can be confounded by environmental factors, lifestyle factors. In the Mendelian randomization technique, what we do is we use randomly allocated genetic variants to study the effect to an exposure.
So, we select these genetic variants because they are related to the exposure of interest. And because these genes are randomly allocated at conception, they're not subject to confounding from environmental or lifestyle factors. Whether you have a gene or not, is not necessarily related to your lifestyle or your environment. And therefore, the association of these genetic variants with certain outcomes isn't subject to confounding.
Dr Carolyn Lam: That makes so much sense, and I suppose that, not to allow cause and effect to be determined. So please, tell us, in this particular case of the anti-hypertensive drugs, what did you do and what did you find?
Dr Dipender Gill: First, we decided specifically which drugs we wanted to look at, and we thought, actually, let's start off with the most commonly prescribed anti-hypertensive drugs. So, we short-listed these based on recent consensus guidelines, and we looked at ACE inhibitors, beta-blockers, calcium channel blockers, thiazide type diuretics. And then, we went back to various online databases to identify which genes correspond to the target protein of these drugs.
We took these genes, and we then identified genetic variants at their specific genetic loci, their specific region of the genome, and we identified the variants in these regions that were also related to systolic blood pressure. And in this way, we inferred that genetic variants, at the protein coding targets of these genes, that were also related to systolic blood pressure, likely represented the effect of variations in these proteins that also implicated blood pressure, and therefore, could serve as proxies, or instruments, to study the effect of these drug targets.
We then went ahead to validate the selection of these genetic variants by forming Mendelian randomization, and specifically, we checked whether people that have genetic variants that correspond to, say, ACE inhibitor activity, or beta-blocker activity, or calcium channel blocker activity, if they also have correspondingly lower risk of coronary heart disease and stroke, to the same degree that we would observe in randomized control trials against placebo.
And indeed, we found that actually, the results were fairly similar, and this gave us confidence. And studying these genetic variants that mimic the effect of these drugs could be used as a proxy or as a surrogate to study their clinical effect of taking these drugs. So, that was the first phase.
Dr Wendy Post: Dipender, congratulations to you and our team. This is a really exciting paper, and the editors were especially interested in the novelty, and the potentially impactful findings, especially of the second part of the study, which I think you'll describe briefly next. And that was using an approach that many who are listening may not have heard about too much before called PheWAS, or a phenome wide association study. And maybe you could tell us briefly what you found in that part of the analysis.
Dr Dipender Gill: The first part, it was very cool, because it allowed us to identify versions of genes that corresponded to the effect of these drugs. But in itself, it didn't tell us anything novel. It didn't tell us anything new. So, the real question was, how could we use this new information to make progress towards helping patients? So, we went back and we thought, "So okay." So, we knew that these drugs are used for certain conditions already to prevent heart disease, to prevent stroke.
But, what about their side effects? What about their repurposing potential? How could we use our new approach to study that a little bit more carefully? As you alluded to, when we used this new technique, relatively new technique called phenome wide association study, and we essentially investigated the association of our genetic variants for each respective anti-hypertensive target with all clinically relevant outcomes throughout the phenome, using the UK bio-back cohort, which was the main population used for this PheWAS, this phenome wide association study.
We were actually able to rapidly investigate over 900 disease outcomes, and their association with our genetic risk score for these drugs. And this was very exciting for us, because it allowed us to very rapidly, efficiently, and cost-effectively explore the potential repurposing opportunity and side effects of these very commonly prescribed drugs, which to our mind, offered significant advantage over previous approaches.
We all know that sometimes randomized control trials can be very expensive and time-consuming, and of course, traditional observational research can be limited by reverse causation, assessment-vise confounding. And so, what we were able to do here had several important advantages, and not to mention the efficiency by which it allowed study of these outcomes.
Dr Wendy Post: Dipender, tell us what you found in your PheWAS study.
Dr Dipender Gill: We identified genetic variants for 3 commonly prescribed anti-hypertensive targets. The first were ACE inhibitors, second, beta blockers, and the third were calcium channel blockers. When performing PheWAS for all of these drug targets, we identified associations with common cardiovascular disease that are related, or implicated in hypertension, specifically hypertension itself, but also circulatory diseases, things like atrial fibrillation, coronary heart disease. They all came up.
And this actually gave us a lot of confidence because that's exactly what we'd expect. We know that these medications prevent or reduce risk of these diseases, and therefore, this served as kind of a positive control that our approach was doing it what it was supposed to do. The novel finding came when we investigated the genetic risk score, or the genetic variants for calcium channel blockers, in this PheWAS approach.
And we actually identified an association which we weren't expecting. We showed that blood pressure reduction through the genetic risk score for calcium channel blockers was an association with an increased risk of diverticulosis, a condition not conventionally thought to be associated with blood pressure. We were very excited and interested by this, and we went on to investigate it further using some other techniques as well.
Dr Wendy Post: The really impactful part of this, many things, but especially this association with diverticulosis. So, maybe you can briefly summarize what you think the potential clinical implications are, and what the next step should be.
Dr Dipender Gill: The first question we had was whether this was related to blood pressure alone, the effect of calcium channel blockers, or perhaps some other effect of these drugs. We investigated the genetic risk score for systolic blood pressure generally and found that this itself wasn't associated with risk of diverticulosis, which suggested that the effect isn't really mediated by blood pressure alone, but it's some other property of calcium channel blockers.
We know that sometimes calcium channel blockers can be associated with constipation, and it may be through this mechanism that they're having consequent effects on risk of diverticulosis. Other possible mechanisms might be through effects on blood flow, through the vasa recta in the bowel. But, what was very interesting was that we went forward with this finding, and investigated, observed, drug use in the UK bio-bank.
Specifically, we looked at people taking non-dihydropyridine, and dihydropyridine calcium channel blockers at baseline, and found that those taking non-dihydropyridine calcium blockers only were known to have a higher risk of diverticulosis as compared to those taking other anti-hypertensive classes, which further added support for our findings. The interesting point here is that looking at the genetics doesn't allow us to discriminate between these drug classes.
That was only possible with the observed data, and that was because the genes for these drug classes were the same.
Dr Carolyn Lam: Well, congratulations. Wow. I'm just so intrigued listening to all of this. Wendy, I would love if you could help put all of this in context for us. The US, the novel information, and the approach that could potentially go way beyond just anti-hypertensive.
Dr Wendy Post: So, this is a very exciting new approach to doing genetic studies that can help us to understand potential targets for therapy in the future, and understanding more about causality, which as Dipender explained, can sometimes be confusing, as it may be confounded by environmental factors. So, using these genetic approaches through Mendelian randomization, and what we heard about today, which is PheWAS, or phenome wide association study, we can learn much more about how the potential observational analyses can be related to new discoveries through mechanisms, or potential side effects, as we heard about here of calcium channel blockers.
So, wanted to congratulate Dipender again with his impactful paper here.
Dr Carolyn Lam: Thanks, Wendy. And then if I could, I'm just going to steal minutes here, because this is so interesting. Where do you think the field's going to go next? And Dipender, with these findings of diverticulitis and diverticulosis, what next? How do we apply this?
Dr Dipender Gill: There's 2 main points to cover here. The first is what we do specifically with the findings we got for calcium channel blockers and diverticulosis. I should emphasize that on their own, I don't think that this should currently change practice. But, I think it should inspire and capitalize further research into this association. If we're able to replicate and validate it further, then perhaps there might be some implications for the drugs that we prescribe with patients at risk of diverticulosis.
The second point I wanted to make is more generally, what does this mean for research, and particularly, genetic research. I think we're living in very exciting times, and there's a lot of really great work that's going to come out using these types of approaches. I think 2 areas that we could expand further is what else we can do with our genetic instruments, or our genetic variants that proxied these drugs. How do we look at other targeted refocusing potential? Can we try and explore other side effects? Can we investigate efficacy for other disease outcomes? Specifically, for these anti-hypertensives.
And the other thing is, which other drugs can we identify genetic variants to proxy? We've been thinking about looking at diabetes medicines. There's a variety of other drugs that correspond to specific gene targets, and proteins. And in theory, these could also be studied using genetics. So, there's a lot more work to come out from this.
Dr Carolyn Lam: Thanks so much, both of you, for joining us today. This was just such an exciting discussion.
Thank you for listening to Circulation on the Run. Don't forget to tune in again next week. This program is copyright American Heart Association, 2019.